Amplifying system



Aug. 26, 1947'.

W. J. FIELD AMPLIFYING SYSTEM Filed Oct. 15, 1943 2 Sheets-Sheet l .PZWimam ON IOMFZOU INVENTO/Y WILL/19M t]: FIELD Aug. 26,1947. w, HELD2,426,497

AMPLIFYING SYSTEM Filed Oct. 15, 1945 2 Sheets-Sheet 2 Imncntor WILL/HMJ. FIELD attorney Patented Aug. 26, 194.

AMPLIFYING SYSTEM William J. Field, Minneapolis, Minn, assignor toMinneapolis-Honeywell Regulator Company, Minneapolis, Minn, acorporation of Delaware Application October 15, 1943, Serial No. 506,313

Claims. 1

This invention relates to electrical amplifying systems and moreparticularly to systems for thermionically amplifying signal impulsesfor the control of other apparatus.

Heretofore, in certain thermionic amplifying systems, it has been commonpractice to supply the plate potentials of the amplifier tubes from arectifying system energized by an alternating current source. In theusual rectifying systems, there has been included a filter network forsmoothing the rectified output thereby to reduce and substantiallyeliminate the alternating current component of the rectifier outputvoltage. To achieve this result, there has been required a relativelyheavy and expensive filter network Which has added to the weight andcost of such systems.

According to the present invention, there is provided an amplifyingsystem in which the alternating current component of the rectified platecurrent supply is advantageously utilized for biasing purposes and as aresult, a low weight, low cost, simplified amplifying system isprovided, capable of excellent result in control service.

It is an object of the invention to provide such an amplifier, and moreparticularly, to provide an improved amplifying system for controlservice capable of being energized from an alternating current.

It is also an object of the invention to provide an amplifying systemwherein the plate potential of the amplifier of one stage has analternating current component which is utilized to produce a desiredbiasing effect in connection with a succeeding stage.

Other and further objects are those inherent in the inventionillustrated, described and claimed.

The invention is illustrated with reference to the drawing in whichFigure 1 is a Wiring diagram of the amplifier system; and

Figures 2 and 3 are wave diagrams illustrating the operation of theamplifier apparatus.

Throughout the illustration and description of the invention, the samenumerals refer to corresponding parts.

In Figure 1, the amplifier system of the invention is illustrated ascontrolling an element, generally designated iii, which may be of anymechanism for example a valve, gate or damper, or a speed, direction,acceleration, volume, position or gas analysis control, requiringphysical movement throughout a range of positions. The positioningmovement of the controlled element in is desired to be made inaccordance with the operation of a responsive element, generallydesignated 30, which is designed so as to be responsive to the conditionbeing controlled and thus as required may be responsive topressure,speed, direction, acceleration, volume, mere position, the analysis ofgases or any other factor or derivative function, which in the end isresponsive to the manipulation of the controlled element [0. Theresponsive element 39 is frequently and indeed usually a low energyinstrument; hence the need for amplification in utilizing the output ofsuch an element.

In the illustrated environment of the present invention, the reversiblemovement for positioning the controlled element I0 is furnished to stemll of the element, by means of a rack and pinion, l2 and 13respectively, or any other suitable mechanical gear. Pinion i3 iscarried upon shaft id and may be driven through reduction gearing I9from a motor, generally designated by the numeral 20.

Motor 20 includes relatively rotatable rotor and stator elements 2! and2223. The element 2| may be of the squirrel cage, wound, or othersuitable type, depending upon the characteristics of the load ofcontrolled element Hi. Windings 22 and 23 are connected together at 2 5and grounded at 25.

Winding 22 is connected so as to be constantly energized from analternating current supply line 2'! through a phase displacingcapacitator 28. The response of the rotor of motor 28 depends upon theenergization of Winding 23 and the direction of the response uponwhether the current through winding 23 in effect leads or lags thecurrent through winding 22. The amplifier system of the presentinvention provides the energizing power supply for winding 23.

The rotation of shaft Hi produced by motor 20 effects the desiredpositioning of the controlled element in and also operates a rebalancingpotentiometer of a resistance bridge generally designated by the numeral46. Bridge 40 includes resistor elements M and 42 which are connected inparallel by leads 43 and M and energized through feeders i5 and 46 froma suitable transformer secondary winding 41. The responsive element 35]mechanically positions a variable tap 33 at selected positions alongresistor ll, in accordance with the condition affecting the responsiVeelement 30 and so selects the operating potential applied to line 34.

The screw threaded end of shaft l5 works in a threaded block it: towhich is secured a blade I! in slidable engagement with resistance 42.

3 Hence, as shaft M rotates in one direction or the other, the blade I1is moved along resistor 42, and so rebalances the bridge 40 ascontrolled element I is brought to its next position.

The amplifier system includes a thermionic amplifier tube or tubes andappurtenances, generally designated 60, a discriminator tube sectionI00, a transformer section I50 and a rectifier section, generallydesignated I18.

In the illustrated embodiment of the inven tion, the amplifier section58 includes two stages of amplification, which may be accomplished inseparate thermionic tubes or in a double tube, generally designated 6|,as illustrated. Tube 6| consists of a single evacuated envelope 62, andcontains two triodes. The first triode constituting thefirstamplification stage comprises an indirectly heated cathode 63, andits cooperating grid 64 and plate 55. The second triode which functionsas the second amplification stage comprises the indirectly heatedcathode 66 together with the latters cooperating grid 61 and plate 68.The cathodes are heated by two filaments 58 and 18 connected in series,one terminal of the series filament circuit being connected to groundedline H and the other terminal supplied by a filament feeder X, which isin turn supplied b a secondary I53 of transformer I50 as hereinafterexplained.

The grid 64 is connected to ground wire H by means of a ballast resistor13, the signal impulse being communicated to the grid by means of Wire34, which is connected through capacitor to the grid lead 16. The gridelement 61 of the second amplifying stage is fed by grid lead 18, thelatter being connected to the ground line 1! by means of a resistor 80and connected through capacitor 82 to junction 83 of the plate circuit85 of the first amplifying stage- From junction 88, there extends aresistor 85, the lower terminal of which is connected by line 81 to theoutput terminal I88 of the rectifier section I10.

A second resistor 90 is connected by line 9i to the junction of resistor85 and line 81, the upper terminal 63 of resistor 00 being connected byline 84 to the plate 68 of the second amplifier stage. Junction 83 ofresistor 80 is the output terminal of the second amplifying stage and isconnected through blocking capacitor 95 to the rid control line 86 andits branch 86'. The

thermionic tubes, generally designated H0 and I constitute thediscriminating tube section I 00 of the amplifier, and each includes anindirectly heated cathode, a control grid, screen grid and plate. Thus,tube IIO includes a cathode II2 which is indirectl heated by filament II I, a control grid II3, screen grid I I4 and plate II5. Similarly, tubeI38 includes a cathode I32, which is indirectly heated by filament I3I,a control grid I33, screen grid I34 and plate I35. The grid II3 of tubeH0 and grid I33 of tube I38 are joined by connection 85 and are fed bythe same grid lead 96. The grid lead 96 is connected to ground wire I40by a capacitor MI and a resistor I42. The wire I is grounded at M3. Theindirectly heated cathode I I2 and one terminal of the heat-- edfilament III are connected to the ground wire I40, and similarly, theindirectly heated cathode I32 and one terminal of its filament heaterI3! are connected together and grounded at I48.

Transformer I58 energizes the system and includes a primary E51, oneterminal of which is grounded at I52, the other terminal being fedthrough an alternating current supply line 21 from a suitable source.The transformer includes a filament heater secondary I53 having oneterminal grounded at I54 and the other terminal feeding supply line X,which is in turn joined to the filament terminal X of each of thethermionic tubes, 8!, H8, I36 and Ill.

Another secondary I55 of the transformer has one terminal connected byline II6 to the plate I I5 of discriminator tube I I 0, the screen gridII4 likewise being connected by means of line II8 to a junction II1 ofthe plate feeder H6. The opposite terminal of the winding I55 isconnected by mean of line I35 to the plate I35 of discriminator tubeI30, screen grid I34 being likewise connected by means of line I38 tojunction I31 on line I36. A center-tap I56 of the winding I55 isconnected by means of line I51 to junction I58 and thence by means ofline I59 to terminal I60 of the motor winding 23. Junction I58 isconnected to cathode I45 through capacitator I82.

Another secondary winding I55 supplies power to the rectifier section,generally designated I10, The rectifier section includes a full-waverectifier tube 01' tubes, generally designated I1I, having cathodesI12-I13, which are indirectly heated by filaments I14. Adjacent thecathodes are the anodes I15 and I16.

Anode I15 is connected by line I11 to one terminal of transformersecondary winding I and anode I16 is connected by line I18 to theopposite terminal of winding I65. The mid-point I85 of the winding I65,is grounded at I61. Th'e cathodes I12I13 of the full wave rectifier tubeI1I are connected to terminal I80, the latter being connected to groundI8I by capacltator I83. The junction I is also connected throughresistor I84 to junction I85, which is in turn connected by line I86 tothe output terminal I88 of the rectifier. Junction I is connectedthrough resistor I88 to the ground line I90 and the output terminal I88is similarly connected through a capacitator I92 to ground.

For clarity in the drawings, the transformer, composed of windings 41and 49 and core 48, for supplying the rebalancing bridge 40, has beenshown as separate from the transformer I50, but the two transformersmay, and in most instances are; a unitary structure. Thussecondaryy/inding 41 is merely added to the transformer I50 and is notseparate.

Operation When alternating current is supplied to feeders 21 and 5I, thesystem is energized and winding '22 of the motor 20 is constantlyenergized. The voltage across winding 22 is displaced in phase withrespect to the voltage across primary I5I by about ninety degrees, dueto the series condenser 28 in the line feeding the motor winding 22.

The rectifier HI and the center tapped secondary I65 function in theusual manner of a full wave rectifier. Thus, during one half cycle,current tends to flow from the upper end of secondary I85 throughconductor I18, anode I16, cathode I13, conductor I82, condenser I83, and

ground connections I8I and I 61 back to the center tap of the secondarywinding I65. During the opposite half cycle, current tends to flow fromthe lower end of secondary I65 through conductor I11, anode I15, cathodeI12, conductor I82, condenser I83, and ground connections I8I and I61back to the center tap of the secondary. Thus, during each half cycle,there is a tendency for current to fiow across condenser I83 in such adirection as to cause a voltage to exist across condenser I83. Thepolarity of the voltage will be such that the upper terminal oicondenser I83 will be positive with respect to the lower terminal. Inother words, a positive voltage will exist between junctions I80 andI8I. The condenser I83 and the condenser I92 cooperate with resistor I84in the usual manner of the condensers and resistors in a filter systemto filter out to a certain extent the alternating current component ofthe rectified current. Thus, referring to Figure 2, curve I95 representsthe voltage across the output terminals of the rectifier before itenters the filter system. The line I91 represents the voltage existingacross the output terminals of the filter system. In other words, thecurve I91 represents the voltage existing across condenser I92. It willbe noted that the voltage represented by line I91 is substantiallyunidirectional with a slight alternating component. Furthermore, thefrequency of this alternating component is twice that of the supplyvoltage. The curve of the supply voltage would be represented by thecurve which would result if the central peak of the three peaks shown inFigure 2 were inverted with respect to the base line. The function ofthe rectifier in producing the voltage represented by line I95 is simplyto invert alternate peaks and to cut off any portion of a voltage curvebelow the base line. If the second peak of the voltage curve I95 isinverted to represent the original alternating voltage curve, it will bequite obvious that the curve I91 has twice as many alternations theoriginal alternating voltage curve.

The magnitude of this alternating component of the voltage representedby line I51 in Figure 2 will depend upon the degree of filtering. Thegreater the amount of filtering, the less pronounced will thisalternating component be. In the ordinary amplifier circuit it isconsidered desirable to employ as many sections of filtering as iseconomically advisable so as to reduce as much as possible thealternating component of the output voltage of the filter system. In thecircuit of the present invention, this filter system is so selected asto produce an alternating component of a magnitude just sufficient togive the desired biasing effect.

Referring now to the operation of the control portion of the apparatus,the various elements are shown in the position they assume when thecontrolled element ID is in the position demanded by the control device30. With the control elements in this position, the positions of sliders33 and I1 correspond so that no voltage exists between them. Thus, nosignal voltage i applied to grid 64. Let it be assumed now that thecondition to which element 33 is responsive changes so as to cause amovement of slider 33 to the right. This will result in an alternatingvoltage existing between sliders 33 and I1 so as to cause an alternatingvoltage to be impressed upon grid 64 through'blocking condenser 15. Theresult of this alternating voltage being applied to the grid 64 is thatthe current flow through the plate circult of the first triode of tube6| has an alternating component corresponding in magnitude and phaserelation to the alternating signal voltage, this current flowing throughthe following plate circuit: from junction I88 through conductor 81,coupling resistance 86, junction 83, conductor 85, plate 65, cathode 63,through the ground connections back to terminal IBI. The current flowingthrough coupling resistance 86 not only has an alternating component dueto the signal voltage but also has an alternating component equal inmagnitude to the alternating component of the output of the filtersystem, as discussed above. The alternating component of the voltageacross resistor 86 is applied to resistor and hence to grid I51 throughthe blocking condenser 82, the blocking condenser functioning in theusual manner to block out any unidirectional component of the voltage.

The plate circuit of the second triode of tube GI may be traced asfollows: from junction I88 through conductors 81 and SI, couplingresistor 93., junction 93, conductor 94, plate 68, cathode (36, throughthe ground connections back to terminal IBI. The current flowing throughresistor 90 will accordingly be a function of the signal voltage asamplified by the first and second triodes of tube BI and a function ofthe unbalance voltage appearing across the output terminals of thefilter network. The nature of this component due to the unbalancevoltage will be dis cussed in more detail later. In any event, thealternating voltage appearing across resistor 93 is impressed throughcondenser 95 on to grids H3 and I33. This voltage will consist primarilyof an alternating voltage representing the amplified unbalance voltageof the bridge as. The magnitude of this voltage will depend upon theextent of displacement of slider 33 with respect to slider I1. The phaseof the unbalance voltage will be dependent upon whether slider 33 hasmoved to the right or to the left of slider I1. Obviously, when slider33 has moved to the right of slider I1, as in the case being considered,the unbalance voltage is displaced in phase from that existing when theslider 33 assumes a position to the left of slider I1. As was noted inconnection with the previously traced circuit connections between thecenter tapped secondary Hi5 and the two tubes III) and I33, the platesH5 and I35 are so connected to the secondary I55 that the voltagesapplied to them are 180 displaced with respect to each other. In otherwords, during any given 'half cycle in which plate I I5 is positive withrespect to cathode H2, plate I35 will be negative with respect tocathode I32. The various circuit constants such as condenser MI andresistor I42 are so selected in value that the amplified unbalancevoltage of bridge II as it appears on grids H3 and I33 will be in phaseeither with the voltage applied to the anode H5 or that applied to anodeI35. Depending upon which anode voltage it is in phase with, one or theother of the tubes III and I33 will become more conductive.

Let it be assumed that under the conditions described in which theslider 33 has been moved to the right with respect to slider I1, theunbalance voltage as applied to grids I I3 and I33 is in phase with theanode voltage applied to anode I I5. Under these conditions, currentwill flow through winding 23 of the motor as follows: from the upperterminal of secondary I55 through conductor IIE, plate II5, cathode IIE,conductor I45, ground connections I43 and 25, junction 24, winding 23,junction I59, and conductors I58 and I51 to center tap I56. During thenext half cycle, obviously no current fiows through the tube IIU sinceplate I I5 is negative with respect to cathode IE2. During the same halfcycle, anode I35 is positive with respect to cathode I32 but the voltageapplied to grids H3 and I33 will be 180 displaced in phase. In otherwords, the grids H3 and I33 will be negative with respect to the oathodeby reason of the signal voltage. Thus, under these conditions, nocurrent will flow through tube I30 and current will flow through tubeIIO only tive. As a result, motor 2| will rotate in a direcduring thehalf cycles in which plate H5 is position opposite to that previouslyconsidered to tive with respect to cathode I I2. The result will movevalve stem ll downwardly and to move be that a voltage is impressedacross winding 23 the threaded block I6 to the left. Themovecorresponding to the voltage output of the half ment of threadedblock I6 to the left will correwave rectifier. Since it is desired toimprove the spondingly move slider IT to the left. Such wave form of thevoltage flowing through windmovement will occur until slider IIcorresponds ing 23 so that it more nearly corresponds to the to theposition of slider 33.

wave form of an alternating current, the con- The operation as describedso far, with the exdenser I62 is connected in parallel with winding 10ception of the presence of the alternating com- 23 through the followingcircuit: from one terponent due to the filtering system, is substanminalof condenser I62 through conductor I40, tially like that of the motorcontrol system disground connections I43 and 25, terminal 24, windclosedin th copending application of Albert P.

ing 23, terminal I 60, and conductor I59 back to Upton, Serial No.437,561, filed April 3, 1942. the other terminal of condenser I62. Thecon- That portion of the operation which is concerned denser I62 byshunting out the higher harmonics with the novel features of the presentapplication tends to cause the curve of the voltage across Will now bedescribed.

winding 23 to be more nearly a sine curve. It will be noted that in thecircuit traced The phase relationship of the voltage across through thefirst triode of tube GI, reference was Winding 23 with respect to thatappearing across made to an alternating component of the voltage winding22 will obviously depend upon Whether due to the alternating componentof the voltage tube III} or tube I39 is conductive since these acrossthe output te m n l o the filter y tubes are conductive during oppositehalf cycles. As previou ly exp ained, this a t rnating ompo- In the casebeing considered, in which the tube hent i l e a f q e y twice that ofthe fre- III! is conductive, the voltage across winding 23 25 l y 0f theSupply Voltage Since this alterwill be 180 displaced from that when tubeI h ting v l pe s r ss res stor 86, it is is conductive. In one case,the current through p d to g d 6 d Will be a e y the winding 23 willlead by approximately 90 that second triode of tube 6 I. Conseq ly, itwill through winding 22 while in the other case, the appear inconsiderably amplified form across current will lag by approximatel 90that 30 resistor 90. Since the plate circuit of the second throughwinding 22. The motor 2I will rotate triode is a so Supplied by thepower supply System i one direction or th other depending upon Ila,there likewise will be introduced an alterwhether the current throughWinding 23 lags or hating eompehent in the voltage across resistor leadsthat through winding 22 In the case be- 99 d to s alternating componentin the voling considered, it will be assumed that the motor age p d o no68- In h r wo d the alrotates in such a direction as to so move rod I5telhatihg component of the Output of the pow r to cause the threadedblock I6 to be moved to ly 10 w ll appear in the v e r s rethe right,This ome mov m nt ill cause th sister 90 in two different forms. One ofthes is stem II of valve I0 to be moved upwardly so as due to theapplication of this alternating comto increase the opening of the valve.The moveponent to the anode 68. The second is due to ment f threaded blk to causes hd [1 t be the application of this alternating component tomoved to the right. Such movement will conplate 65 and que tly to grid61 of the second tinue until the slider I1 corresponds in positiontriode- This Second component will be d to slider 33, at which time, novoltage will exist placed in phase h r p t o th first and will betweensliders 33 and I1. When this happens, -15 be very much greater than thefirst due to the the voltage impressed upon grids H3 and 133 amplifyingeiiect of this second triode. In fact, ill posses no component derivedfr bridge due to the voltage gain of the second triode, the 40 and forreasons presently t be described, y portion of the voltage component dueto the presthe tube Ho nor tub I30 l be Conductive ence of thisalternating component in the volt- Thus winding 23 will b deenergiz dand motor age applied to plate 58 can be disregarded. Due 2I will stop.The apparatus is so designed that to the fact that both grids 64 d 5 a eonthis Wi l occur when the controlled element In nected to cathodes 63and 66, current will flow has assumed a position corresponding t th t inthe first and second triodes at all times so that therethrough will be180 displaced in phase from crosses the cathode vo demanded bytheresponsiveelement 30 this alternating voltage will be present at all Itwill be obvious from the above that if slider imes. This alternatinvolta e will in urn be 33 is moved to the left, the voltage betweenapplied through bl g Condenser 5 t0 grids sliders as and I! will be 180displaced from that and v reason f t p ase reversin which existed in thecase just considered. As a action between the first and Second S s ofresult, the voltage impressed upon grids H3 and amplification and byreason of the phase shift- I33 will be similarly 180 displaced in phase.As mg action of condensers 95 and and resistor a result, the Voltageapplied t grids 3 and 3 I42, this voltage will be so related to thevoltages will no longer be in phase with the anode voltage applied toanodes I and that it tends to applied to plate II5, but, on the otherhand, will drive grids 3 and I33 e ative durin t ose he in phase withthat applied to anode I35. As portions of the anode voltage cycles inwhich e a result, only tube I38 will be conductive so that 65 anode smost Positive h respect 0 the c current will flow through winding 23 asfollows: In othel Words, referring o F ure 3, the from the lowerterminal of secondary I55 through Voltage due to the a p d alternatingVoltage conductor I36, plat I35, cathode I32, ground existing across theoutput terminals of the filter connections I48 and 2-5, terminal 24,field windystem is represented in co siderab y exagger ing 23, terminalI an, and conductor I59 and I5! ed form by the curve 2M. The voltageapplied to the center tap of secondary I55. As a result of to plate H5is represented by the curve 202 and current flowing through thiscircuit, winding 23 that applied to plate I35 b the curve 203, It willagain be energized, but the current flowing will be noted that at thepoint a, the curve 20I ltage line so that the efthat just consideredwhen tube II 0 was conducfoot of this voltage from point a to point I)while anode I35 is positive, is to drive the grids I I3 and I33negatively. Similarly, the voltage curve 2M is below the cathode voltageline between points and d so that when anode H5 is positive the eifectof this voltage is likewise to bias the grid negative with respect tothe cathode. Due to the fact that th voltage is of twice the frequencyof the voltage applied to the anodes H5 and I35, it is thus possible tohave an alternating voltage function so as to bias the grids negativewith respect to the cathodes during both half cycles. Quite obviously,if the grid voltage were of the same frequency as the anode voltage, itcould be elfective to bias the grid negatively only during one of eachtwo half cycles. With the present arrangement, however, it so functionsduring both half cycles. It is true that between points I) and c, forexample, the effect of this voltage is to drive the grid positive withrespect to the cathode. During this portion of the anode voltage cycle,however, the anod voltage is relatively low so that there is very littletendency for the tube to pass current even though the grid may be at ahigher potential than the cathode. Furthermore, due to the tendency ofthe anodes and screen grids to emit when hot and thus cause current tofiow through condenser MI during the half cycles in which the anodes arenegative, there is a considerable tendency for a charge to be built upon condenser I4I of such polarity as to cause the grids to be biasednegatively. Because of this, any current flow that takes place throughtubes I I0 and I30 in the absence of a signal from the bridge 40 isnegligible.

It will be thus seen that I have devised an arrangement in which it ispossible to reduce the amount of filtering that is necessary in the D.C. power supply and to utilize the resulting ripple in an advantageousmanner to bias the grids of the final output tubes. The constants of thefiltered network are so selected that the unfiltered alternating rippleis of such a value and phase as to give the correct amount of bias.Obviously, if it is too great, it will tend to counteract the effect ofa small unbalance voltage from bridge 4|. By properly selecting theconstants of the filter circuit, however, it is possible to obtain theexact amount of bias that is necessary and at the same time to reducethe cost of the filter circuit.

While I have shown a specific embodiment of my invention, it is to beunderstood that this is for purposes of illustration only and that myinvention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. An electronic discriminator circuit comprising a plurality ofelectronic discharge devices each comprising an anode, a cathode, and acontrol element, means for applying alternating Voltages of the samepredetermined frequency but of opposite phase relationship to the anodesof said devices, means for so applying signal voltages to the controlelements of both devices that one or the other of said devices becomesconductive, the device that is conductive depending upon thecharacteristics of the signal voltages, and further means for applyingto the control elements of both devices an alternating biasing voltageof twice the predetermined frequency, of a magnitude independent of theanode current, and of such phase relationship with respect to thealternating voltages applied to the anodes of said devices that saidbiasing voltage is effective over the intermediate portions of thepositive 10 half cycles of the anode voltages applied to both anodes tobias the control elements negatively with respect to the cathodes.

2. An electronic phase discriminator comprising a plurality ofelectronic discharge devices each comprising an anode, a cathode, and acontrol element, means for applying alternating voltages of the samepredetermined frequency but of 0pposite phase relationship to the anodesof said devices, means for applying signal voltages of the samefrequency and the same phase relationship to the control elements ofboth devices so that one or the other of said devices becomes conductivedepending upon the phase relation of the signal voltage to the anodevoltage of that device, and further means for applying to the controlelements of both devices an alternating biasing voltage of twice thepredetermined frequency, of a magnitude independent of the anodecurrent, and of such phase relationship with respect to the alternatingvoltages applied to the anodes of said devices that said biasing voltageis effective over the intermediate portions of the positive half cyclesof the anode voltages applied to both anodes to bias the controlelements negatively with respect to the cathodes.

3. An electronic discriminator comprising a plurality of electronicdischarge devices each comprising an anode, a cathode, and a controlelement, means including a source of alternating voltage for applyingalternating voltages of the same predetermined frequency but of oppositephase relationship to the anodes of said devices, means for so applyingsignal voltages to the control elements of both devices that one or theother of said devices becomes conductive, the device that is conductivedepending upon the characteristics of the signal voltages, and furthermeans including a full wave rectifier energized by said source ofalternating voltage for applying to the control elements of both devicesan alternating biasing voltage of twice the predetermined frequency andof such phase relationship with respect to the alternating voltagesapplied to the anodes of said devices that said biasing voltage iseffective over the intermediate portions of the positive half cycles ofthe anode voltages applied to both anodes to bias the control elementsnegatively with respect to the cathodes.

4. In a multi-stage amplifier, first and second electronic dischargedevices, each having an anode, a cathode, and a controlelement, a sourceof alternating voltage, means comprising a rectifier and a filter systemoperatively connected to said source for obtaining therefrom aunidirectional voltage having a small component of alternating voltage,means for applying a signal voltage to the control element of said firstelectronic discharge device, means for connecting said rectifier andfilter system to the anode of said first discharge device so as to forman anode circuit, means for applying voltage derived from said lastnamed anode circuit to the control element of said second electronicdischarge device, whereby the voltage applied to said control element ofsaid second electronic discharge device has a component due to thesignal voltage and an alternating component derived from said rectifierand filter system, means for applying an alternating potential derivedfrom said alternating source of power to the anode of said secondelectronic discharge device, and means for maintaining a phaserelationship between the alternating component of the voltage applied tothe control element of said second discharge device and derived from therectifier and filter network and the alternating potential applied tothe anode such that said alternating component is effective to applysufficient biasing voltage to said control element of said second devicethat in the absence of a signal voltage said second discharge device issubstantially non-conductive during the entire cycle.

5. In a multi-stage amplifier, first and second electronic dischargedevices, each having an anode, aoathode, and a control element, a sourceof alternating voltage, means comprising a full wave rectifier and apartial filter system operatively connected to said source for obtainingtherefrom a unidirectional voltage having a small component ofalternating voltage of twice the frequency of said source, means forapplying a signal voltage to the control element of said firstelectronic discharge device, means for connecting said rectifier andfilter system to the anode of said first triode so as to form an anodecircuit, means for applying voltage derived from said previously namedanode circuit to the control element of said second electronic dischargedevice, whereby the voltage applied to said control element of saidsecond electronic discharge device has a component due to the signalvoltage and an alternating component derived from said rectifier andfilter system, means for applyin an alternating potential derived fromsaid alternating source of power to the anode of said second electronicdischarge device, and means for maintaining a phase relationship betweenthe alternating component of the voltage applied to the control elementof said second discharge device and derived from the rectifier andfilter network and the alternating potential applied to the anode suchthat the alternating voltage applied to the control element of saidsecond discharge device is effective to bias the grid negatively duringthat portion of the conductive half cycle in which the anode potentialis greatest.

6. In a multi-stage amplifier, first, second, and third electronicdischarge devices, each having an anode, a cathode, and a controlelement, a source of alternating voltage, means comprising a full waverectifier and a partial filter system operatively connected to saidsource for obtaining therefrom a unidirectional voltage having a smallcomponent of alternating voltage of twice the frequency of said source,means for applying a signal voltage to the control element of said firstelectronic discharge device, means for connecting said rectifier andfilter system to the anode of said first and second triodes so as toform anode circuits therefor, means for applying a voltage derived fromthe anode circuit of said first device to the control element of saidsecond electronic discharge device whereby the voltage applied to saidcontrol element of said second electronic discharge device has acomponent due to the signal voltage and an alternating component derivedfrom said rectifier and filter system, means for applying a voltagederived from the output circuit of said second discharge device to thecontrol element of said third discharge device, means for applying analternating potential derived from said alternating source of power tothe anode of said third electronic discharge device, and means formaintaining a phase relationship between the alternating component ofthe voltage applied to the control element of said third. dischargedevice and derived from the rectifier and filter network and thalternating voltage applied to the anode such that the alternatingvoltage applied to the control 12 element is efiective to bias thecontrol element negatively with respect to the cathode.

7. In a multistage electronic amplifier, a source of alternatingvoltage, a final stage comprising two electronic discharge devices eachcomprising an anode, a cathode, and a control element, said anodes beingoppositely connected to said source of alternating voltage, said controlelements of said discharge devices being connected together into acommon input circuit, means including a voltage amplification stage forapplying a control voltage to said common input circult and for causingone or the other of said electronic units to be rendered conductivedepending upon a characteristic of said control voltage, means includinga source of pulsating unidirectional voltage for energizing said voltageamplification stage, said last named means being effective to introduceinto said control voltage an alternating component due to the pulsationsin said unidirectional voltage, and means for maintaining a phaserelationship between said alternating component and said source ofalternating voltage such that said alternating component is effective tobias the control elements of said electronic discharge devicesnegatively with respect to their cathodes durin the intermediateportions of both half cycles of the anode voltage.

8. In a multistage electronic amplifier, a source of alternatingvoltage, a final stage comprising two electronic discharge devices eachcomprising an anode, a cathode, and a control element, said anodes beingoppositely connected to said source of alternating voltage, said controlelements of said discharge devices being connected together into acommon input circuit, means including a voltage amplification stage forapplying a control voltage to said common input circuit and for causingone or the other of said electronic units to be rendered conductivedepending upon a characteristic of said control voltage, means includinga full wave rectifier and a partial filter system connected to saidsource of alternating voltage for energizing said lt amplificationstage, said last named means being effective to introduce into saidcontrol voltage an alternating component due to the ripple in the outputof said partial filter system, and means for maintaining a phaserelationship between said a1- ternating component and said source ofalternating voltage such that said alternating component is effective tobias the control elements of said electronic discharge devicesnegatively with respect to their cathodes during the intermediateportions of both half cycles of the anode voltage.

9. In a multistage electronic amplifier, a source of alternatingvoltage, a final stage comprising two electronic discharge devices eachcomprising an anode, a cathode, and a control element, said anodes beingoppositely connected to said source of alternating voltage, said controlelements of said discharge devices being connected together into acommon input circuit, means including a voltage amplification stage forapplying a control voltage to said common input circuit and for causingone or the other of said electronic units to be rendered conductivedepending upon a characteristic of said control voltage, means includinga full wave rectifier and a partial filter system connected to saidsource of alternating voltage for energizing said voltage amplificationstage, said last named means being efiective to introduce into saidcontrol voltage an alternating component due to the ripple in the outputof said partial filter system, and means for maintaining a, phaserelationship between said alternating component and said source ofalternating voltage such that said alternating component is effective tobias the control elements of said electronic discharge devicesnegatively with respect to their cathodes during the intermediateportions of both half cycles of the anode voltage, the filter systembeing so designed that said ripple is of such magnitude as to producethe desired amount of bias.

10. In a multistage electronic amplifier, a source of alternatingvoltage, a final stage comprising two electronic discharge devices eachcomprising an anode, a cathode, and a control element, said anodes beingoppositely connected to said source of alternating voltage, said controlelements of said discharge devices being connected together into acommon input circuit, means including a voltage amplification stage forapplying an alternating control voltage to said common input circuit,said control Voltage being reversible in phase for causing one or theother of said electronic units to be rendered conductive depending uponthe phase of said control voltage, means including a full wave rectifierand a partial filter system connected to said source of alternatingvolt- 14 age for energizing said Voltage amplification stage, said lastnamed means being efiective to introduce into said control voltage analternating component due to the ripple in the output of said partialfilter system, and means for maintainin a phase relationship betweensaid alternating component and said source of alternating voltage suchthat said alternating component is effective to bias the controlelements of said electronic discharge devices negatively with respect totheir cathodes during the intermediate portions of both half cycles ofthe anode voltage.

WILLIAM J. FIELD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,297,836 Levy Oct. 6, 19422,330,377 Phair Sept. 28, 1943 2,121,987 Rosenberg June 28, 19382,128,070 Bahls Aug. 23, 1938 2,376,513 Shafier May 22, 1945 2,375,599Jones May 22, 1945

